This invention relates to a device for decreasing radial forces caused by shaft bendings in rotor dynamic machines such as centrifugal pumps.
The rotating impeller in such a pump is exposed to radial forces, reaction forces from the surrounding pump housing. These forces, which are caused by the pressure of the medium flowing through the housing, are not always uniformly allocated along the periphery. Therefore, a resultant force occurs which influences the impeller and the pump shaft in a certain radial direction.
It is possible to form the pump housing so that by a certain volume flow and a certain head, the resultant of the radial forces will be practically zero. As a pump, however, has to work under varying conditions, radial forces will appear. It then appears that the resultant force has one direction when the pump is working with a maximum volume flow and a low head and another direction when the pump is working with a minimum volume flow and a high head. Of these two cases, the latter results in the strongest resultant force.
The theory described above relates to impellers with one or several vanes. Impellers with one vane (one-channel impeller) are also exposed to a rotating force.
The disadvantages caused by the above mentioned radial force are that the pump shaft must be dimensioned for the maximum radial force in order to avoid shaft damages, diminish the bearing load, secure the function of the shaft seals and diminish the wear on the seal that usually is arranged between pump housing and impeller at the pump inlet.